1. Technical Field
The present invention relates to a method for producing an L-amino acid using a microorganism, and more specifically, to a method for producing an L-amino acid, such as L-lysine, L-threonine, and L-glutamic acid, etc. L-lysine and L-threonine are typically used as animal feed additives, health food ingredients, amino acid infusions, etc., and L-glutamic acid is typically used as a seasoning. Therefore, these are industrially useful L-amino acids.
2. Background Art
L-amino acids are industrially produced employing fermentation methods using microorganisms of the genera Brevibacterium, Corynebacterium, and Escherichia, etc. (EP0857784, 0999267, 1170358, JP11-192088A, WO00/53726, WO96/17930, WO03/04674). Wild-type microorganisms, artificial mutants of said bacterial strains, and microorganisms which have been modified so that the activities of the L-amino acid biosynthesis enzymes are enhanced by recombinant DNA techniques are typically used for L-amino acid production.
Known methods for enhancing the ability of various strains to produce an L-amino acid include modifying the L-amino acid uptake or export. For example, to modify the uptake, the ability to produce L-amino acids is enhanced by deleting or reducing the L-amino acid uptake into the cell. For example, one approach is to delete or lower L-glutamic acid uptake by deleting the gluABCD operon or a part of the operon (EP1038970), etc.
One of the methods for modifying the export of an L-amino acid is to delete or reduce the export of an L-amino acid biosynthetic intermediate, and another method is to strengthen the L-amino acid export. For the former, if the target amino acid is L-glutamic acid, reducing the export of α-ketoglutarate, which is an intermediate in the biosynthesis of L-glutamic acid, by mutating or disrupting the α-ketoglutarate permease gene has been reported (WO01/005959).
To delete or reduce the export of an L-amino acid biosynthetic intermediate, methods for overexpressing genes responsible for L-amino acid export have been reported, for example, producing L-lysine (WO97/23597) or L-arginine using a bacterial strain of a microorganism of the genus Corynebacterium with enhanced expression of the L-lysine or L-arginine export gene (LysE) (Journal of Molecular Microbiology Biotechnology (J Mol Microbiol Biotechnol) 1999 November; 1(2):327-36). Furthermore, increasing the expression of the rhtA, B, and C genes (U.S. Pat. No. 6,303,348), or the yfiK, yahN genes, etc. has been reported as a method for producing L-amino acids in an Escherichia bacteria (EP 1013765).
Aside from modifying the L-amino acid biosynthesis pathway and modifying the uptake and export of the L-amino acid as described above, modifying the ability of the bacteria to take up sugar is another example of a method for improving L-amino acid production. For example, the phosphoenolpyruvate:carbohydrate phosphotransferase system (hereinafter, also referred to as PTS: phosphotransferase) is widely known as a transporter which functions to uptake sugar. Furthermore, PTS is classified as a substrate-independent common system EI (encoded by ptsI), HPr (encoded by ptsH), or substrate-specific component EII. Glucose-specific EII is encoded by ptsG and crr, with the crr gene being a part of an operon with ptsH and ptsI. One known method for producing an L-amino acid uses the genus Escherichia in which the ptsG gene has been enhanced (WO03/04670), and another method uses the genus Escherichia in which the ptsH, ptsI, and crr genes have been enhanced (WO03/04674).
Aside from the glucose PTS mentioned above, the bglF gene is known to encode β-glucoside specific phosphotransferase (PTS) (Journal of Bacteriology, 1999, Vol. 18, No. 2, p 462-468, Biochemistry, 1998, Vol. 37, p 17040-17047, Biochemistry, 1998, Vol. 37, p 8714-8723), but the use of a gene encoding PTS other than glucose PTS for the production of an L-amino acid has not been reported.